Submerged membrane bioreactors are one of the fastest growing treatment methods in wastewater. However, as is typical of all wastewater treatment processes, it is often the effectiveness of the preliminary liquids/solids separation operation, early in the influent journey that determines the efficiency of downstream processes.
Membrane bioreactors combine key aspects of the activated sludge treatment process with a physical membrane liquids/solids separation operation. The membrane component uses low pressure microfiltration or ultra filtration membranes to eliminate the need for clarification and tertiary filtration. Generally, the membranes are immersed in the aeration basin, although some applications use a separate membrane tank.
Aging infrastructure, more stringent effluent requirements and changing population demographics have driven dramatic growth in membrane bioreactors both in North America and throughout the World. Their increasing popularity results from the ability of bioreactor technology to achieve filtration at the micron level, as well as its ability to deliver high quality effluent in considerably less space than a conventional wastewater treatment plant.
However, when planning a bioreactor based treatment plant, one must balance preliminary liquids/solids separation options with issues such as cost, footprint, and energy consumption. Even though membrane bioreactors technology is continuing to evolve and make improvements in the cost-of-ownership equation, today it is widely recognized that the cost of building and operating a membrane bioreactor is typically higher than that of conventional processes. This additional cost is often mitigated, however, by the proven benefits of membrane bioreactors.
While there are several types of membrane units, each depend on the preliminary liquids/solids separation operation of mechanical screening. Membranes are particularly vulnerable to non-biological suspended solids. These solids are a natural part of wastewater and arrive at the treatment facility in the form of trash, hair, plastics, rags, and other physical contaminants. Such contaminants cause fouling or blockages as well as matting among the membrane fibers. The results of this fouling can range from increased energy consumption and permanent damage to the membrane, causing its removal from service.
Fouling also causes other compromises in operation capabilities, including restrictions to processing capacity, costs and time for backwashing, and plant downtime when off line for replacement or maintenance. It is the screening system that typically accounts for less than three one-hundredths of the membrane bioreactor investment that must remove these potentially damaging physical contaminates from the process prior to introduction of the flow into the membrane tank. It is the screen that must ensure material capture without bypassing or carryover to the downstream and it is the screen and its efficacy that determines the demand for downstream maintenance.
The perforated plate of the instant invention mitigates the problems of current perforated plate prior art devices. For example, the perforated plate of this invention does not use any dynamic seals that are subject to wear and failure. Seal failure results in downstream contamination which causes tangling or fouling of sensitive membrane filters. The orientation of the perforated plate of this invention to the flowing water in the water channel provides an efficient and simple installation and provides a passive cleaning mechanism that eliminates the need for maintenance intensive brushes
Thus, it would be valuable to have a screening system that would not have the problems set forth above.